1. Field of the Invention
The present invention relates to an active noise cancellation apparatus for actively reducing road noise.
2. Description of the Related Art
It is known that road noise is generated due to wheel vibration derived from road surface roughness being transmitted to a floor panel and the like and causing the floor panel and the like to vibrate. Apparatus for actively reducing this road noise are described in PTLs 1 to 4.
The apparatus of PTLs 1 to 3 cancel road noise by detecting an acceleration as a reference signal by an acceleration sensor placed on a suspension, detecting acoustic pressure in a vehicle interior as an error signal by a microphone, and outputting control sound (secondary sound) by a speaker placed in the vehicle interior. PTL 2 also mentions that a vibration generator is placed on a floor panel to generate a secondary sound.
The apparatus described in PTL 4 comprises a vibration generator placed on a floor panel, uses vibration of a suspension as a reference signal and vibration of the floor panel as an error signal, and controls the vibration generator so as to reduce the error signal. The patent literature states that road noise can be reduced by suppressing vibration of the floor panel by this vibration generator control.